Current transformers having multiturn primary windings



May 2351967" .sp y r-n-uzv v 3,321,725. v

CURRENT TRANSFORMERS-HAVING MULTI-TURN 'PRIMARY wuwmes Filed Dec. 1e, 1965' 2 Sheets-Sheet 1 ,May 23, 1967 i R. SCANNEY CURRENT TRANSFORMERS HAVING MULTI-TURN PRIMARY wmnmes Filed Dec. 16, 1965 2 Sheets-Sheet '2 United States Patent 3,321,725 CURRENT TRANSFORMERS HAVING MULTI- TURN PRIMARY WINDINGS Robert S. Canney, Berwick, Maine, assignor to General Electric Company, a corporation of New York Filed Dec. 16, 1965, Ser. No. 514,221 Claims. (Cl. 336-173) This invention relates to current transformers and more particularly to current transformers having multi-turn primary windings.

In many types of current transformers the primary winding is in the form of a bar or other conductor extending through a window opening in the cast core and secondary winding unit. These transformers are very satisfactory for their intended use. However, in many current transformers it is necessary to provide a number of turns of the primary winding to obtain the desired ratio of current transformation.

In the present manner of manufacturing current transformers having multi-turn primary windings, it is necessary to fix the ratio of transformation of the transformer prior to casting or enclosing the unit in the outer casing. In many instances the outer casing is a resinous insulating material. This has required the manufacturers to stock a comparatively large number of current transformers of various ratios. The alternative to stocking a large variety of ratios has been to manufacture current transformers according to customer orders. As will be understood, such a manufacturing technique leads to very uneven pro duction and lengthens the time required to fill customers orders. Further, due to the uneven production it normally increases the cost of the transformer. It has long been considered desirable to manufacture multi-turn primary transformers which could be substantially completed for stocking but which would not have the ratio of the transformer determined until taken from stock in response to a customers order. This would relieve the manufacturer of the necessity of stocking a large variety of transformers and enable orderly use of the production facilities. 7

It is, therefore, one'object of this invention to provide a current transformer having a multi-turn primary winding which may be substantially completely manufactured and stocked without a predetermined ratio.

A further object of this invention is to provide a current transformer having a multi-turn primary winding which may be adjusted to any of a plurality of ratios.

A still further object of this invention is to provide a current transformer having a multi-turn primary winding comprising a plurality of individual conductors which can be terminated in any desired manner to provide any of a plurality of transformer ratios.

Briefly, in one form this invention comprises a current transformer having a core and secondary winding unit encased in a resinous material to form a single unit. A plurality of primary conductors are placed through the window opening of the core and secondary winding unit. A second plurality of primary conductors are placed about the outside of the core and secondary winding unit substantially parallel to the first plurality of primary conductors. End caps are provided, secured to the core and secondary winding unit, holding the primary conductors in the desired position. The entire device .is then enclosed in an insulating casting resin to provide a current transformer having a plurality of primary conductors extending from each end thereof. The primary conductors may then be terminated to provide a current transformer of a desired ratio.

The invention which is sought to be protected will be particularly pointed out and distinctly claimed in the ice claims appended hereto. However, it is believed that this invention and the manner in which its various objects and advantages are obtained, as well as other objects and advantages thereof, will be more fully understood by reference to the following detailed description of a preferred embodiment thereof, particluarly when taken in connection with the accompanying drawing, in which:

FIGURE 1 is a perspective view of the transformer portion of a current transformer according to this invention;

FIGURE 2 is an exploded perspective view of a current transformer according to a preferred form of this invention prior to casting in an insulated resin;

FIGURE 3 is a perspective view of a current transformer according to the preferred embodiment of this invention showing one form of termination of the primary conductors; and

FIGURES 4 and 5 are end views of each end of a current transformer according to this invention showing one form of termination of the primary conductors to obtain 7 a desired ratio.

Reference will now be made to the drawing in which like numerals are used to indicate like parts throughout the various views thereof. The current transformer of this invention, as shown in the preferred embodiment, I

comprises a core and secondary winding unit which is cast as a single unit, a plurality of primary conductors extend through and around the core and secondary winding unit with the primary conductors terminated as necessary to provide any of a variety of transformer ratios. Referring first to FIG. 1 of the drawing, there is shown the transformer portion 10 of a current transformer having primary terminals 12 and 14 at each end of unit 10. Secondary leads 16 extend from bottom 18 to a secondary terminal box (not shown). As will be understood, transformer 10 is usually mounted on a high voltage bushing (not shown) with the secondary leads 16 brought through such bushing to the secondary terminal box at the bottom of the bushing. The current to be monitored is provided to the transformer ll) through the primary terminals 12 and 14.

Referring now to FIG. 2 of the drawing, there is shown an exploded perspective view of one form of the current transformer according to a preferred embodiment of this invention. A cast core and secondary winding unit 20 is shown having a Window opening 22 therein. Secondary leads 16 extend from the bottom of the core and coil unit 20. One group of primary conductors 24 extend through the window opening 22. A second group of primary conductors 26 are preferably formed substantially in a hat-shape, as shown, and are placed around the outside of the core and secondary winding unit 20. A pair of end caps 28, only one being shown in the drawing, are secured to opposite ends of the core and winding unit 20. End caps 28 have a plurality of slots 30 and 32 for receiving primary conductors 24 and 26 respectively. The end cap 28 holds conductors 24 and 26 in a predetermined position within and around the core and secondary winding unit 20. End caps 28 are also provided with a plurality of studs 34 for securing a terminating ring 36 and a terminal bell 38 to each end of the transformer 10.

After the primary conductors 24 and 26 are secured in position through the end caps 28, the entire unit is enclosed in a resinous insulating material, as indicated at 39 in FIG. 3 of the drawing. This will provide a current transformer unit substantially as shown in FIG. 3. However, primary conductors 24 would extend from transformer 10 substantially parallel to the conductors 26. in the manner shown in FIG. 2. The current transformer unit 10 could then be tested and placed in stock without terminating the primary conductors 24 and 26.

When an order is received for a certain ratio the primary conductors 24 and 26 would be terminated by attaching terminating rings 36 to end caps 28 by means of studs 34, in the manner particularly shown in FIG. 3. One or more tabs 40 are provided on terminating rings 36 and the primary conductors 24 and 26 are secured to the rings 36 and to each other to provide the desired transformer ratio. After the primary conductors 24 and 26 have been terminated as desired, terminal bells 38 are secured to the ends of the transformer by means of studs 34 providing units substantially as shown in FIG. 1. As will be understood, studs 34 provide an electrical connection betwen terminal bells 38 and terminating rings 36.

As will be understood any desired number of primary conductors 24 and 26 may be provided and the conductors may be connected in series and/ or in parallel as necessary to provide any desired transformer ratio. FIGURES 4 and 5 show an end view of each end of transformer 10, showing one form of termination. In FIGS. 4 and 5 twenty-four primary conductors 24 and twenty-four primary conductors 26 are shown. Terminating rings 36 are shown with a single tab 40 to which one of the primary conductors 24 is connected, for example, as by welding. As can be seen from FIGS. 4 and 5 a twenty-four turn primary is provided by connecting all of the primary conductors 24 and 26 in series. Obviously, if desired, a plurality of tabs 40 could be provided and twelve conductors could be connected in parallel to provide a two-turn primary.

One advantage of the disclosed construction occurs when testing of the unit discloses a turn-to-turn failure in the primary conductors 24 and 26. This could occur, for example, due to the shifting of conductors 24 and 26 during the casting of the unit in the resinous insulating material. Such transformer having a turn-to-turn failure may still be used by merely selecting a transformer ratio which would place the two turns in parallel. In this manner it is possible to use many transformers which would otherwise either have to be scrapped or else be subjected to expensive re-work.

From the above it will be apparent that by means of this invention there is provided a current transformer having a m-ulti-turn primary winding which will fulfill all of the objects and advantages previously set forth. It will of course be understood by those skilled in the art that many changes may be made in the preferred embodiment hereinbefore set forth without departing from the spirit and scope of the invention, particularly as it is defined in the appended claims.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. A current transformer having a multi-turn primary winding comprising a core and secondary winding unit having a window opening therein, a first plurality of primary conductors extending through said window opening, a second plurality of primary conductors extending around the outisde of said core and secondary winding unit, end caps secured to opposite ends of said core and secondary winding unit, said end caps provided with slots for receiving said first and said second plurality of primary conductors and holding them in position within and around said core and said secondary winding unit.

2. A current transformer as claimed in claim 1 in which a resinous insulating material is molded about said core and secondary winding unit, said first and said second plurality of primary conductors, and said end caps.

3. A current transformer as claimed in claim 2 in which terminating rings are provided on opposite ends of said core and secondary winding unit for terminating said first and said second plurality of primary conductors to provide a desired ratio.

4. A current transformer as claimed in claim 2 in which said end caps are provided with a plurality of studs, terminating rings are provided being secured to said end caps by said plurality of studs, said terminating rings terminating said first and said second plurality of primary conductors to provide a desired transformer ratio.

5. A current transformer as claimed in claim 3 in which terminal bells are provided on opposite ends of said core and winding unit, said terminal bells secured to said terminating rings and electrically connected thereto, said terminal bells having terminals thereon as the primary terminals of said current transformer.

No references cited.

LEWIS H. MYERS, Primary Examiner. 

1. A CURRENT TRANSFORMER HAVING A MULTI-TURN PRIMARY WINDING COMPRISING A CORE AND SECONDARY WINDING UNIT HAVING A WINDOW OPENING THEREIN, A FIRST PLURALITY OF PRIMARY CONDUCTORS EXTENDING THROUGH SAID WINDOW OPENING, A SECOND PLURALITY OF PRIMARY CONDUCTORS EXTENDING AROUND THE OUTSIDE OF SAID CORE AND SECONDARY WINDING UNIT, END CAPS SECURED TO OPPOSITE ENDS OF SAID CORE AND SECONDARY WINDING UNIT, SAID END CAPS PROVIDED WITH SLOTS FOR RECEIVING SAID FIRST AND SAID SECOND PLURALITY OF PRIMARY CONDUCTORS AND HOLDING THEM IN POSITION WITHIN AND AROUND SAID CORE AND SAID SECONDARY WINDING UNIT. 